1. Field of the Invention
This invention pertains to novel latent catalysts for promoting reaction between vicinal epoxides and phenols and/or carboxylic acids (or anhydrides of such acids). Such reactions are commercially important in that functional monomers (e.g. hydroxyethyl acrylate), hydraulic fluids (e.g. 2-phenoxyethanol) and high molecular weight linear or cross-linked epoxy resins are thus produced.
2. Description of the Prior Art
The reactions between epoxides and phenols and/or carboxylic acids (or anhydrides) have been extensively studied and many patents have issued which describe these well known classes of reactants. See, for example, U.S. Pat. Nos.:
______________________________________ 2,216,099 3,377,406 3,547,885 2,633,458 3,477,990 3,694,407 2,658,885 3,547,881 3,738,862 ______________________________________
Canadian Pat. No. 893,191, German Pat. No. DT 2,206,218, and the text "Handbook of Epoxy Resins" by H. Lee and K. Neville, McGraw Hill, N.Y. (1967).
In addition to describing the classes of reactants, the above patents also show that (1) a catalyst is required to attain a satisfactory reaction rate and (2) those skilled in the art recognize that the reaction between epoxides and phenols is not, mechanistically speaking, the same as the reaction between epoxides and carboxylic acids (or anhydrides) due to the differences in products. The latter point is illustrated by the fact that substantially linear polymers are produced (U.S. Pat. No. 3,477,990) by reacting epoxy resins with polyfunctional phenols in the presence of a catalyst whereas cross-linked polymers are produced (U.S. Pat. No. 3,547,885) by reacting the same epoxy resins with a polycarboxylic acid (or anhydride) in the presence of the same catalysts. The reactive species which catalyzes the reaction is therefore believed to be different in each instance. Thus, compounds which catalyze one reaction would not necessarily be expected to catalyze the other.
Several problems have been encountered in using many of the prior art catalysts. In many instances, the catalysts react with the epoxy reactant and thus preclude the option of marketing a blend comprising an epoxy resin and a catalyst; this blend is commonly referred to as a "precatalyzed epoxy resin". In other instances, the problem associated with the prior art catalysts is selectivity; i.e. the catalysts simultaneously promote the reaction between the epoxy reactant and the phenolic hydroxyl group (or acid group) on the reactant and the aliphatic hydroxyl group(s) on the product giving branched or cross-linked polymers rather than the desired linear polymers. In still other instances, the reaction rate is unsatisfactory and/or the product is highly colored and therefore unsatisfactory for many uses and/or the product was contaminated with corrosive anions (e.g. chloride) and is therefore unacceptable for electrical encapsulationf (potting).
These and other problems have now been solved by the subject invention.